FL cells were harvested from E16 to 17 C/EBPα^−/− mice and cultured in SCF/TPO/Flt3L/IL-6 for 48 hours. The cells were washed and pelleted and then resuspended in medium containing C/EBPα-GFP, and GFP-expressing retroviral particles (3×). GFP⁺ cells were sorted by flow cytometry 48 hours after the last infection. Cells were plated in soft agar colony assays at 1.25 × 10⁴ cells/plate according to the procedures described in “Materials and methods.” Colony formation was evaluated after 7 days, and results are presented as the mean number of colonies ± the standard error.